Electric heating device



Oct; 20, 1942. I J. L. RYCROFT 2,299,596

ELECTRIC HEA'I'I NG DEVICE Filed Dec. 9, 1959 INV N R x40 Zamkrf 19cm}? Patented Oct. 20, 1942 ELECTRIC HEATING DEVICE John Lambert Rycroft, Northwood, England, as-

signor to The General Electric Company Limited, London, England Application December 9,

In Great Britain 12 claims.

This invention relates to electric heating devices more particularly for use in cooking ranges and of the kind formed from sheet metal.

An electric heating device according to one embodiment oi the present invention comprises one or more sheathed wire heating elements keyed into a groove or grooves in a plate of'sheet metal. According to another embodiment of this invention, an electric heating device comprises one or more resistors embedded in insulating refractory material and wholly or partly enclosed in a sheath or sheaths, the whole being keyed into a groove or grooves in a plate of sheet metal. The

sheath may comprise a metal tube of complete or incomplete cross-sectional circumference, and the element may be arranged on or beneath the surface of the plate.

The base of the groove or grooves is preferably flattened, and sheet metal channels or strips may be arranged between the external walls of the grooves in such a way as to form with the fiattened bases of the grooves a substantially con tinuous fiat surface to facilitate cleaning. If channels are used they may be filled with refractory material.

Alternatively or additionally, a fiat surface suitable for use as the active surface of a hot plate may be obtained by arranging the sheaths to have a fiat surface flush with the ungrooved surface of the plate.

One construction of hot plate in accordance with the invention and the method of manufacture thereof will now be described by way-of example with reference to the accompanying drawing, of which Figure 1 is a cross-sectional view of a circular grooved plate before insertion of the heating elements, Figure 2 is a view of the underside and Figure 3 a cross-sectional view of the completed plate, and Figure 4 is a cross sectional view of the insulator through which leads are brought out from the ends of the resistors, while Figures 5 and 6 are two views of one of the metal sheaths employed in this construction, and Figure 7 is a cross-sectional view of one of the metal rings used to fill the space between the grooves.

Referring firstly to Figure 1, the circular plate I of heat resisting material such as the metal known under the tradename Inconel, is formed with a depending rim 2 and four concentric grooves 3 of U-shape in cross-section. A circu- -lar depression I is also formed in the centre of the plate. Four circular sheaths 5 of nickel or other suitable metal, of which one is'shown in 1939, Serial No. 308,445

December-.12, 1938 (Cl. 219-37) Figures 5 and 6, are provided, each having a different radius corresponding to the radius of one of the grooves 3. The sheaths are each of the cross-sectional form shown in Figure 6, having a flat base and an opening 6 sulating refractory material 1 into the sheaths.

through which in- (Fig. 3) is inserted A resistor 8 of spiral form is embedded in the refractory material, the ends being brought out through holes 9 in a block of insulating material l0 (Fig. 4), sponds with holes H in the sheath. The block I0 is attached to the sheath by a bolt 12 passing through a hole I; in the sheath, and a nut H. The sheath is completely filled with refractory material, and inserted in the corresponding groove 3 in the plate I, with the opening 6 at the bottom of the groove. Four metal rings ii of channel section, as shown in Fig. 7, are arranged in the spaces between the grooves 3 and between the inner groove and the dished portion 4. The whole assembly is then compressed between two fiat surfaces and is flattened into the form shown in Figure 3. The elements com prising the resistors 8, refractory material I and sheaths 5, and the rings 15 are thus securely keyed in position, the bases of the rings l5 and of the grooves 3 forming a continuous fiat surface which forms the active surface of the hot plate.

In an alternativ construction, the reverse side of the plate may form the active surface, the depending rim 2 and the insulating blocks Ill being then disposed on the opposite side to that shown in Figure 3. In this case part of the sheaths will be exposed, and the sheaths are preferably arranged to enclose the resistor completely.

It will be realized that the invention is not confined to hot plates only; for example a device similar to that described above may form the base of a kettle. A device according to the invention need not be of circular form, but may have any other convenient shape, thus a long rectangular shaped strip may be, used for oven heating-or as a clamp on heater, or a specially shaped plate may be used for a flat iron heater.

Iclaim:

' 1. An electric heating device comprising at least one resistor embedded in insulating refractory material and at least partly enclosed in a sheath, the whole being keyed into a fiat-bottomed groove in a plate of sheet metal, and sheet metal channels arranged between the external walls of the groove and having a fiat surface flush with the base of the groove.

2. An electric heating devic comprising at least one resistor embedded in insulating refractory material and at least partly enclosed in a which corre- I th groove.

3. An electric heating device comprising at least one resistor embedded in insulating refractory material and at least partly enclosed in a sheath, said sheath being keyed into a groove in a single plate of sheet metal and having a flat surface flush with the ungrooved surface of the plate, said groove having a closed end and an open end, the closed end being disposed over said sheath, the closed end of said groove being wider than the open end thereof, the sheath in which said heating elements is disposed being negatively shaped to the contour of said groove and closely fitted therein whereby said sheath 'is locked in said plate.

4. A method of producing an electric heating device comprising the steps of embedding at least one resistor in refractory material in a sheath, inserting the sheath in a groove in a sheet metal plate, the width of said groove at all portions from its closed to its open end not exceeding the width of said open end, and keying the sheathed resistor in position in the plate by subjecting the plate to-compressionbetween two surfaces, to alter the shape of said groove by causing at least one portion thereof to have a width greater than that of said open end and to deform said sheath to ne atively correspond and closely fit to the altered contour of said groove, whereby said sheath is locked in said plate.

5 A method of producing an electric heating device comprising the steps of embedding at least one resistor in refractory material in a sheath, inserting the sheath in a suitably shaped groove in a sheet metal plate, arranging sheet metal channels between the external walls of the groove, and keying the sheathed resistor and the channels in position in the plate by subjecting the plate to compression between a plane surface and a cooperating surface.

6. An electric heating device comprising a plurality of side-by-side sheathed wire heating ele vments fitting closely into a plurality of side-byside. grooves in a single plate of relatively thin sheet metal of substantially uniform thickness and retained therein by deformation of said grooves, said grooves being joined by fiat ungrooved surface portions of said plate, which portions lie in a single plane.

'7. An electric heating device comprising a plurality of side-by-side resistors each embedded in insulating refractory material and partly enclosed in a separate sheath, said sheaths fitting closely into a plurality of side-by-side grooves in a single plate of relatively thin sheet metal ofv substantially uniform thickness and retained therein by deformation of said grooves, said grooves being joined by flat ungrooved surface portions, which portions lie on a single plane.

8, An electric heating device comprising a plurality of resistors each embedded in insulating refractory material and at least partly enclosed in a sheath fitting closely into a fiat-bottomed groove in a plate of relatively thin sheet metal of substantially uniform thickness, and sheet metal channels arranged between the external walls of the grooves and each having a flat surface flush with the bases of the adjoining grooves, the said sheathed resistors and the said channels being retained in position by deformation of the grooves.

9. An electric heating device comprisinga plurality of resistors each embedded in insulating refractory material and at least partly enclosed in a sheath fitting closely into a fiat-bottomed groove in a plate of relatively thin sheet metal of substantially uniform thickness, and sheet metal channels filled with refractory material arranged between the external walls of the grooves and each having a flat surface flush with the bases of the adjoining grooves, the said sheathed resistors and the said channels being retained in position by deformation of the grooves. Y

'10. An electric heating device comprising a plurality of side-by-side resistors each embedded in insulating refractory material and at least partly enclosed in a separate sheath, said sheaths fitting closely into a plurality of side-by-side grooves in a single plate of relatively thin sheet metal of substantially uniform thickness and retained therein by deformation of said grooves,

'. said grooves being joined by flat ungrooved surface portions, which portions lie on a single plane,

\ each of said sheaths having a fiat surface flush with said flap ungrooved portions.

11. A method-of producing an electric heating device comprising the steps of embedding each of a plurality of resistors in refractory material in separate sheaths, inserting said sheaths in a plurality of closely fitting side-by-side grooves in a relatively thin single sheet metal plate of substantially uniform thickness, and keying the sheathed resistors in position in the plate by subjecting the plate to compression between two surfaces and thereby deforming the said grooves to lock said sheaths in said plates and to join said deformed grooves by fiat ungrooved surface portions lying in a single plane.

12. A method of producing an electric heating device comprising the steps of embedding each of a plurality of resistors in refractory material in a sheath, inserting the sheath in a closely fitting groove in a relatively thin sheet metal plate of substantially uniform thickness, arranging sheet metal channels between the, external walls of the grooves, and keying the sheathed resistors and the channels in position in the plate by sub- 

